Impedance type electronic relay



July 29, 1958 M. E. HoDGEs Erm. 2,845,581

IMPEDANCE TYPE ELECTRONIC RELAY original Filed April 11, '1955Inventors: Mevwg'n E. Hod

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es Harold T. Seeleg United States Patent O IMPEDANCE TYPE ELECTRONICRELAY Merwyn E. Hodges, Philadelphia, and Harold T. Seeley,

Havertown, Pa., assignors to General Electric Company, a corporation ofNew York Original application April 11, 1955, Serial No. 500,475.Divided and this application August 8, 1956, Serial No. 602,886

Claims. (Cl. 317-36) This invention relates to an electronic relay, andmore particularly to an impedance type electronic relay for initiating apreselected control operation in response to predetermined impedanceconditions of an electric power transmission line.

This application is a division of copending patent application S. N.500,475, Merwyn E. Hodges and Harold T. Seeley, tiled on April 1l, 1955,and assigned to the present assignee.

The trend today in the iield of electric power, principally perhaps forreasons of economy, is to operate high voltage transmission lines atloads which approach system stability limits. In order to maintainstability and preserve continuity of service to the electric powerconsumers, it is increasingly desirable in present day electric powertransmission applications to provide protective relaying systems capableof extremely high speed response. A protective relaying system whichwill respond to any fault condition on a transmission line within onecycle (based on the typical power system frequency of 60 cycles persecond) would contribute greatly to the prevention of major systeminterruptions and to the mitigation of damage caused by a fault. Toavoid the inherent time delay caused by inertia during the operation ofconventional electromechanical relays, protective relays employingelectronic elements have been designed'.

As is well known to those skilled in the art of protective relaying, ahigh voltage transmission line is usually protected by distance relayingor by a pilot relaying system, or by both. An example of a pilotrelaying system wherein extremely high speed electronic relays are usedis set forth and claimed in a copending application S. N. 473,802, ledon December 8, 1954, by Merwyn E. Hodges, Norman A. Koss and Harold T.Seeley and assigned to the present assignee. In protecting an electricpower transmission line, a relaying problem may be introduced by theeffects of power swings, i. e., surges of power in the electric powersystem resulting from the removal of a fault condition located withinthe system but external to the protected transmission line, or resultingfrom the loss of synchronism between a generator and the system. A powerswing may cause the fault responsive protective relays to operate. Incertain relaying applications it may be desirable to block operation ofthe relays and thereby prevent tripping of the transmission line circuitbreaker during power swings. In other relaying applications it may bedesirable to permit relay operation but to block reclosing of thecircuit breaker. Accordingly, it is an object of this invention toprovide an improved relay for performing a preselected control operationin an electric power transmission line protective relaying system inresponse to a power swing.y

It is a further object of this invention to provide in a protectiverelaying system employing electronic relays, an improved relay havingelectronic elements and responsive to an electric power swing forinitiating a preselected control operation.

Another object of this invention-is to provide a rean impedance typeelectronic relay for an electric power transmission line. This relay isresponsive to an operating quantity comprising a voltage related to thetransmission line current by a first preselected constant impedance anda restraining quantity comprising the vectorial difference between avoltage proportional to the transmission line voltage and a voltagerelated to the line current by another preselected constant impedance.We provide electronic level detecting means to produce output voltagewhenever the magnitude of the operating quantity exceeds that of therestraining quantity which indicates that the impedance condition of thetransmission line is within the operating region of the relay. Theoutput voltage energizes a selectively controlled time delay circuitwhich, after a predetermined time interval, performs a preselectedcontrol operation, such as blocking the tripping signal of an associatedfault detecting relay.

Our invention will be better understood and further objects andadvantages will be apparent from the following description taken inconjunction with the accompanying drawing, in which:

Fig. 1 is a schematic diagram, partly in block form,

of a transmission line protective relaying system which embodies apreferred form of the impedance type electronic relay; and 4 Figs. 2aand 2b are graphical representations of the operating characteristics ofthe protective relays illustrated in Fig. l, with Fig. 2a havingimpedance coordinates and Fig. 2b having voltage coordinates.

Referring now to Fig. l, we have shown by way of illustration a 3-phasetransmission line, represented by conductors 11, 12, and 13 which iscoupled to a supply source of electric power by a 3-pole circuit breaker14. The transmission line may be of the type employed in an electricpower system to conduct 3-phase alternating current of power frequency,such as 60 cycles per second, from the supply source to a remote load,not shown, at a very high voltage, e. g., 330,000 volts phase-t0- phase.Although we do not wish to be limited thereto, we have shown in Fig. 1,by way of example, distance relaying equipment arranged to trip circuitbreaker 14, thereby disconnecting the transmission line from the supplysource, immediately upon the occurrence of a phase fault, i. e., a shortcircuit between phase conductors at some point along the transmissionline, within a predetermined distance from circuit breaker 14. In thismanner the transmission line is protected from the damaging effects ofprolonged fault current. Circuit breaker 14 and the protective relaysillustrated in Fig. 1 are located at what will be referred tohereinafter as the local terminal of the transmission line.

As can be seen in Fig. l, a pair of instrument current transformers 15and 16 and a pair of instrument potential transformers 17 and 18 arecoupled to a pair of the conductors connecting circuit breaker 14 to the3-phase supply source. The secondary circuits of these instrumenttransformers are connected to the protective relays to supply theretocurrent and voltage quantities which accurately reflect the current andvoltage conditions existing at the local terminal. A tripping relay 19,shown in block form, is connected to these instrument transformers andproduces an output control signal in response to certain conditions ofline current and voltage which indicate that a phase fault has occurredon the protected transmission line. In the illustrated embodiment of ourinvention, tripping relay 19 is a distance type relay which has beenconnected to respond to phase faults involving transmission lineconductors 11 and 12. It should be understood that by providing anadditional current and potential transformer together with two morerelays similar to relay 19, the transmission line can be adequatelyprotected for phase-to-phase fault conditions involving any two of itsthree conductors. There are many suitable distance type relays, ofeither electronic or the conventional electromechanical construction,that may be used satisfactorily for tripping relay 19. At present weprefer to use an extremely high speed m-ho type electronic relay such asfully described and claimed in the aforesaid copending patentapplication S. N. 473,802 filed by Merwyn E. Hodges, Norman A. Koss andHarold T. Seeley. The relay referred to will produce an output controlsignal of positive unidirectional voltage in less than .014 second inresponse to a phase fault within its reach.

The output control signal of tripping relay 19 is conveyed by aconductor 20 to a blocking relay 29, and thence by a conductor 21 to acontrol relay 22. The blocking relay 29 which will be described indetail hereinafter, supervises the output control signal of the trippingrelay 19 in a manner and for reasons to be explained below. Controlrelayy 22, which has been shown in block form in Fig. l, operates toconvert the output control signal of relay 19 into a suitable trippingsignal for energizing a trip coil 23 of circuit breaker 14, and by meansof control relay 22 the output control signal may be utilized toinitiate other preselected control functions. Any suitable circuitarrangements may be used for performing this control relay function. Anexample of suitable circuits employing electronic elements to obtainextremely rapid response is described and claimed in a copending patentapplication S. N. 471,593, tiled on November 29, 1954, by Merwyn E.Hodges and assigned to the present assignee. The tripping signal outputof control relay 22 is supplied to trip coil 23 via a conductor 24 andan auxiliary switch 25 of circuit breaker 14. Energization of the tripcoil 23 actuates a latch 26 thereby releasing switch member 27 of thecircuit breaker for rapid circuit interrupting movement. As switchmember 27 moves to its open circuit position, auxiliary switch operatesto interrupt tripping current thereby deenergizing trip -coil 23.

In certain electric power systems, as a result of power swings, whichare power surges such as caused by the removal of a short circuitcondition external to the protected transmission line, or by the lossvof synchronism between a generator and the system, the tripping relay19 may operate to give a false indication of a phase fault. It may bedesirable to provide means to prevent or block the output control signalof relay 19, thereby preventing tripping of circuit breaker 14, whenevera power swing is in progress, or to provide means to prevent or blockreclosing of circuit breaker 14 after it has tripped. To illustrate theeffect of a power swing, reference `should be made to Fig. 2a which is aconventional impedance diagram. Abscissa R and ordinate jX of Fig. 2adescribe values of resistance and inductive reactance respectively asdetermined by the vectorial relationship between transmission linevoltage and current measured at the local terminal. The ratio oftransmission line voltage to current defines impedance looking into thetransmission line from the local terminal and is designated apparentimpedance. iX are scaled equally and in the same units, such as ohms, ona phase-to-neutral basis. The transmission line has a determinableimpedance which is represented on Fig. 2a, by way of example, as theprotected line. A circle LT represents the locus of impedance valueswhich dene the operating limits or reach of a typical mho type distancerelay used as tripping relay 19. Whenever the apparent impedance of thetransmission line, as indicated by current and voltage quantitiessupplied to relay 19 by the instrument transformers, falls within thearea cir- Both coordinates R and lll cumscribed by locus LT, relay 19will respond to produce an output control signal.

It is well known to those skilled in the art that under normal loadconditions the apparent impedance of the transmission line will falloutside the operating region or reach of relay 19 as defined by locusLT, while upon the occurrence of a phase fault condition on thetransmission line within a predetermined distance of the local terminal,the apparent impedance will substantially instantaneously change to avalue which will cause relay 19 to operate. On the other hand, a uniquecharacteristic of a power swing is that the apparent impedance of thetransmission line changes relatively slowly. In other words, therelationship of line voltage and current at the local terminal during apower swing changes at a slow rate while approaching the criticalrelationship between these quantities, as defined by locus LT, at whichtripping relay 19 will operate. The succession of apparent impedancevalues during a typical power swing has been shown on Fig. 2a, by way ofexample, by line PS. A measurable length of time is required for theapparent impedance to change from a point such as A to `a point A alongline PS during a power swing. To block the output control signal ofrelay 19 during a power swing, therefore, we provide relay 29, to bedescribed below, which has an operating characteristic, as defined bylocus LB, circumscribing locus LT of tripping relay 19. Relay 29includes a time delay arrangement to delay blocking of the outputcontrol signal until after relay 19 has opportunity to perform itstripping function in case of a true fault condition. A similararrangement, not shown, could be used to block only the reclosing ofcircuit breaker 14.

In the illustrated embodiment of our invention, the means provided toblock or prevent the output control signal of tripping relay 19 fromreaching control relay 22 whenever a power swing in the electric powersystem is in progress comprises an impedance type electronic relay 29.The operating characteristic or reach of this blocking relay has beenrepresented in Fig. 2a, by way of example, by a circle LB ywhichcircumscribes circle LT of relay 19. Circle LB is the locus of impedanceValues which define the operating limits of blocking relay 29. Themanner in which the blocking relay operates can best be demonstrated byreference to Fig. 2b, which is a graphical representation of itsoperating characteristic in terms of voltage. Figure 2b has beenconstructed by multiplyingdthe ohmic coordinates R and jX of Fig. 2a bycurrent I owing in the transmission line from the supply source towardthe load. Abscissa IR and ordinate jX of Fig. 2b describe values ofresistive and reactive components respectively of voltage produced bycurrent As can be seen in Fig. 2b, the operating characteristic ofblocking relay 29, defined by locus LB, comprises a circle having aradius of IZr wherein Zr is an impedance of predetermined magnitudebuilt into the relay in a manner to be described presently. The origin Oof `circle LB is offset from origin O by the vector TZ-k,

where k is a predetermined vector impedance built into the relay in amanner to be described presently. The vector IZk is disposed atapproximately degrees from the IR axis. The vector V shown in' Fig. 2bis a voltage in the relay that represents transmission line voltage atthe local terminal during normal load conditions, and

accordingly is proportional to current multiplied by the apparentimpedance through the load. Within the blocking relay voltage Lik, whichis hereinafter referred to as the offset voltage, is vectoriallysubtracted from voltage V to derive a net voltage FI7--IFZ--k which isutilized to restrain operation of the relay. Whenever the magnitude ofthe net voltage' V-'Zdk becomes less than voltage IZr, the apparentimpedance of the transmission line is within locus LB, and the blockingrelay operates to produce a signal voltage.

Since relay 29 in effect responds to a predetermined magnitude of thevector difference between apparent impedance as a predetermined constantimpedance, it is an impedance type relay. The voltage signal produced asdescribed above energizes a time delay circuit which, after apredetermined time interval, operates to block the output control signalof tripping relay 19. If a true phase fault occurs on the protectedtransmission line, both the tripping and blocking relays operatesubstantially simultaneously, and the output control signal produced byrelay 19 is able to pass to control relay 22 by virtue of the time delayadded to the blocking operation, thereby causing circuit breaker 14 totrip. But if a typical power swing has caused blocking relay 29 tooperate, by the time the apparent impedance of the transmission line haschanged from point A to point A along line PS shown in Fig. 2a, and themho tripping relay can operate in response thereto, the time delaycircuit has operated and passage of the output control signal to controlrelay 22 is prevented.

The circuitry of a preferred embodiment of the impedance type blockingrelay 29 is shown in Fig. l and will now be described. As can be seen inFig. l, we

- provide suitable transforming means 30, preferably comprising a pairof primary windings 30a and 30b, a pair 0f secondary windings 30C and30d, and a common iron core 30e which has at least one air gap. Theprimary windings 30a and 3017 `are connected in the secondary circuitsof the 2-phase star-connected current transformers and 16 respectively.These two primary windings have an equal number of turns and arearranged in opposing relationship whereby net ampere turns in thetransforming means 30 is determined by the vectorial difference betweenthe, transmission line currents owing in conductors 11 and 12. Thus, theprimary windings 30a and 30b eifectively simulate a single primarywinding supplied by current from delta-'connected current transformers.The currents flowing in conductors 11 and 12 during balanced conditionshave equal magnitudes but are 120 electrical degrees out-of-phase, andthe difference current in these conductors is V3i where I represents themagnitude of current owing in the conductors.

Transforming means 30 derives across each secondary winding 30C and 30da voltage representative of the difference current in transmission lineconductors 11 and 12 both in magnitude and phase over the operatingrange of current while imposing minimum burden on current transformers15 and 16. The magnitude of voltage across each secondary winding andthe phase angle by which it leads the net current in the primarywindings is determined by the amount of load in the secondary circuits.Open circuit secondary voltages lead the net current by 90 electricaldegrees. The effective secondary load resistance in the illustratedembodiment of our invention is preselected to cause the secondaryvoltages to lead the difference current by 60 electrical degrees. Due tothe high percentage of total primary current used for magnetizing ironcore 30e and its air gap, initial transient D.C. offset in fault currentwave form will not be appreciably reproduced in the secondary voltage.The transforming means 30 also serves as a desirable means forinsulating succeeding relay circuits from the current transformerconnections.

Because the succeeding relaying circuits are designed to operateover awide range of current magnitudes, it is possible that during a faultcondition of maximum current an extremely large voltage may be inducedin the secondary windings 30e and 30d. To prevent injury to theinsulation of the secondary windings which might otherwise be damaged bysuch a large voltage, voltage limiters 31 and 32 are connected acrosssecondary wind- 6 ings 30e` and 30d respectively. Each voltage limiterhas a non-linear current-voltage characteristic, that is, the ohmicvalue of the limiter decreases with increasing voltage applied across itso that current will increase at a greater rate than voltage. Many suchnon-linear current-voltage characteristic devices are known in the art,and for the purposes of the illustrated embodiment of our invention weprefer at present to use a special ceramic resistance materialcomprising silicon carbide crystals held together by a suit- Y ablebinder, such as described and claimed in U. S. Patent 1,822,742, issuedto Karl B. McEachron on September 8, 1931. Each limiter, 31 or 32,provides means for increasing secondary load as the respective secondaryvoltage increases thereby limiting the maximum possible peak value ofsecondary voltage to a safe level Without interfering with measurementaccuracy at the normally smaller values of voltage.

Transforming means 30 is loaded by an adjustably tapped resistor 33connected across secondary winding 30e. of resistor 33, as determined bythe position of a slider 33a, has a fixed relationship to the diferencecurrent producing this voltage. This lixed relationship is in units ofohms and is termed replica impedance. The particular magnitude of thisreplica impedance is Zr. During balanced system conditions, themagnitude of voltage across the tapped portion of resistor 33 is\/'3IZr.

It should be recognized that this voltage divided by \/3 is the radiusof the circle characteristic of the impedance relay as shown in Fig.2b.l (The coordinates of Figs. 2a: and 2b are scaled on the conventionalphase-to-neutral basis, i. e., values of impedance and voltagerespectively, are measured along one conductor from the local terminalto the neutral point of the load. Since the apparent impedance of thetransmission line is necessarily measured ona phase-to-phase basis, itis necessary, during balanced conditions, to use a conversion factor ofl/\/3 when reproducing the voltage quantities detected at the localterminal on the graphical representation of Fig. 2b.) Slider 33a isadjusted to obtain the desired magnitude of Zr, which magnitude, for thepurposes of the illustrated embodiment of our invention, preferably isequal to about 3A the impedance of the transmission line protected bytripping relay 19.

As shown in Fig. l, transforming means 30 is loaded by anotheradjustably tapped resistor 34 connected across secondary winding 30d. Inaddition, a rheostat 35 is provided `across winding 30d to permit ashift of the phase relationship of derived voltage with respect to thenet current in the primary windings. The iixed relationship of voltageappearing across the tapped portion of resistor 34 to the diiferencecurrent producing this voltage is replica impedance Zk. The voltageacross the tapped portion of resistor 34 is \/3ik during balancedconditions. It should be recognized that this voltage vector divided by\/3 determines the location of the center O of the circle characteristicLB as shown in Fig. 2b in terms of phase-to-neutral voltage. Theresistance value of rheostat 35 is selected to obtain the desired phaseangle characteristic of replica impedance ik, and a slider 34a of tappedresistor 34 is adjusted to obtain the desired magnitude of ik. For thepurposes of the illustrated embodiment of our invention, a phase angleof 60 degrees and a magnitude of approximately 1/z the diameter ofcircle LT permit an adequate and consistent margin to be maintainedbetween locus LB and the locus LT of a typical mho type tripping relay.By making Z`k` equal to zero, the center of locus LB could be shifted tothe origin O of Fig. 2b.

The voltage between transmission line conductors 11 and 12 is suppliedvia the 2-phase star-connected potential transformers 17 and 18 tosuitable transforming The voltage appearing across the tapped portion i7means 36 in the impedance blocking relay 29. This transforming meanscomprises, for example, an iron core transformer 36 having a primarywinding 36m connected to potential transformers 17 and 18 and asecondary winding 36b as illustrated in Fig. 1. Transformer 36 derivesacross its secondary winding a voltage which represents the transmissionline voltage between conductors 11 and 12 both in magnitude and phase,and also insulates succeeding relay circuits from the potentialtransformer connections. During balanced system conditions the derivedvoltage is V3, where V is directly proportional to the transmission linephase-to-neutral voltage. One terminal of secondary winding 36b isconnected to a lead 37 and the other terminal is coupled to tappedresistor 34 in a manner to develop between lead 37 and slider 34a a netvoltage comprising voltage \/3lk subtracted from voltage VV.' Themagnitude of net voltage \/3(V-IZk) appearing between lead 37 and slider34a divided by \/3 has been shown in Fig. 2b.

During a power swing the electric power system will remain substantiallyin balance, and, therefore, we obtain correct operation of the impedanceblocking relay by supplying it with the current and voltage quantitiesderived from conductors 11 and 12 only. For convenience, hereafter inthis specification We will refer to the voltage across the tappedportion of resistor 33 merely as IZr, and the voltage between slider 34mand lead 37 tect the rectifier from damaging high voltage levels. f

Limiter 40 may be similar to lirniters 31 and 32 described above. Asvoltage lZ rises to excessively high values, the resistance of limiter40 becomes less and a nonlinearly increasing voltage drop is producedacross resistor 39 thereby limitingthe voltage level at rectifier 38.

A loading resistor 41 is connected in parallel with voltage limiter 40to reduce the magnitude of voltage available at rectifier 38 by a xedpercentage of IZr during normal, relatively low voltage levels. Thisfixed percentage is selected so that the magnitude of the unidirectionaloperating voltage will be just equal to the resulting magnitude ofrestraint voltage, which appears across resistor 45 as explained below,whenever the magnitude of V-IZ/c is equal to IZr.

Voltage V-IZk is utilized to restrain operation of the impedanceblocking relay. This voltage is supplied to Suitable rectifying means,such as the full-wave bridge type rectifier 42 illustrated in Fig. l,where it is converted to a more useful unidirectional voltage. A voltagelimiting circuit comprising a resistor 43 and a voltage limiter 44,similar respectively to resistor 39 and voltage limiter 41B describedabove, is provided between tapped resistor 34 and rectifier 42 toprotect the rectifier from damaging high voltage levels. connectedbetween the positive and negative D.C. terminals of rectifier 42. Thepositive D.C. terminal of rectifier 42 is connected to a negative busrepresented by the symbol (Thesymbols -1- -and are used throughout thedrawing to represent the posi-tive bus and negative bus respectively ofa unidirectional supply voltage source, such as a battery, which has notbeen shown for the sake of drawing simplicity.) The unidirectional.voltage appearing across resistor 45 is smoothed by a filter capacitor46, and this voltage, which comprises the A resistor 45 is restraintvoltage yof the blocking relay, is related to D.C. terminal of rectifier38 is connected by a lead 48 to the input circuit of a level detector 49which has been shown in block form in Fig. 1. For the purposes of thisspecification the term level detector is used to designate a device suchas an electronic switch, i. e., means responsive to an input signal ofat least a predetermined instantaneous value for producing substantiallyinstantaneously an output signal of predetermined constantcharacteristic. Any suitable circuit can be used for level detector 49.For example, a particularly well suited circuit arrangement is shown inFig. 1 of a copending patent application S. N. 500,475 filed on Aprilll, 1955, by Merwyn E. Hodges and Harold T. Seeley and assigned to thepresent assignee. This circuit, which is described in detail and claimedin the aforementioned application, has the desirable features ofextremely fast pickup and cutoff times, selectable pickup with respectto input signal level, and a high degree of accuracy which is maintainedduring fluctuations of supply voltage and variations of ambienttemperature. The input circuit of level detector 49 provides a D.C. pathfrom lead 48 to negative bus. Thus, a closed path or loop for directcurrent fiow is formed by negative bus, rectifiers 42 and 38, and theinput circuit of level detector 49. Since the operating and restrainingvoltages are applied in opposition, direct current will liow into theinput circuit of level detector 49 and develop a positive unidirectionalsignal voltage between lead 48 and negative bus only when the magnitudeof operating voltage is greater than the magnitude of restrainingvoltage. Level detector 49 produces a large magnitude output voltagesubstantially instantaneously when energized by only a very smallpredetermined magnitude of this positive signal voltage.

A filter capacitor 50 is connected between lead 48 and negative bus andsmooths the signal voltage. Rectifier 47 prevents direct current liow inthe closed loop as long as the magnitude of restraining voltage isgreater than the' magnitude of operating voltage, as is the case undernormal system conditions. Therefore, filter capacitor 50 normally has nocharge, and when system conditions change so that operating voltageexceeds restraining voltage, the time required by capacitor 50 to chargefrom zero to the predetermined magnitude of signal voltage can beaccurately taken into account in determining the overall operating timeof the relay.

The operation of blocking relay 29 to produce an output voltage at leveldetector 49 will now be summarized. Assume that a power swing has causedthe transmission line apparent impedance to come within the operatingregion of the relay as defined by locus LB. The vector V representingtransmission line voltage minus the offset voltage Ik will then haveless magnitude than the resulting transmission line current I multipliedby the predetermined constant impedance Zr. Consequently, therestraining voltage across resistor 45 is less than the operatingvoltage output of rectifier 38 and a positive signal voltage is producedthereby energizing level detector 49. Zr and Zk have been selectedwhereby locus LB is substantially concentric with the mho tripping relaylocus LT, as can be seen in Fig. 2a, and whereby the margin maintainedbetween these circles is sufficient to permit proper operation of thetime delay circuit, described below, during any power swing.

As can be seen in Fig. l, the output voltage of level detmector 49 isconveyed by a lead 51 to a control grid 52C of a cathode follower vacuumtube 52.' Cathode 52a 'of tube 52 is connected to negative bus through acathode resistor 53 comprising a pair of voltage dividing resistors 53aand 53h. The cathode heater and heater circuits, being well known tothose skilled in the art, have been omitted for the sake of drawingsimplicity. The anode or plate of tube 52 is connected directly topositive bus. The output voltage of level detector 49 energizes controlgrid 52e which causes conduction in tube 52 to increase from itsquiescent value. A resultant unidirectional voltage drop is developedacross cathode resistor 53, and the portion of this resultant voltageappearing across resistor 53b provides an input signal for thesucceeding time delay circuit.

The time delay circuit of the impedance blocking relay operates anelectromagnetic relay 54. A normally closed permissive contact 55 ofrelay 54 interconnects conductors 20 and 21 whereby the output controlsignal of tripping relay 19 is conveyed to control relay 22. Thus, theoutput control signal can be blocked by energizing relay 54 to openpermissive contact 55. Although other suitable time delay circuits maybe used, we have illustrated a selectively controlled time delay circuitdescribed and claimed in the aforesaid copending application of MerwynE. Hodges, S. N. 471,593. In this circuit two triode vacuum tubes, 56and 57, are provided to control the energization of electromagneticrelay 54. Tube 56 operates to energize relay 54 while tube 57 operatesto suppress or disable tube 56 thereby preventing energization of relay54. The plate of tube 56 is connected through the operating coil ofrelay 54 to positive bus, and the cathode of tube 56 is connectedthrough a cathode resistor 58 to negative bus. The input signal takenfrom resistor 531) supplies the control grid 56e of tube 56 through anR-C time delay circuit comprising resistor 59 and capacitor 60.

The plate of tube 57 is connected directly to positive bus while thecathode of tube 57 is connected through the common cathode resistor 58to negative bus. The control grid 57a` of tube 57 normally is suppliedby a positive voltage derived from a voltage dividing network connectedbetween positive and negative buses comprising a resistor 61 in seriescircuit with a resistor 62 in series circuit with a resistor 63 which isin parallel with the impedances to negative bus of the circuits incontrol relay 22 coupled to conductor 21. Grid 57e is connected to thecommon point of resistors 61 and 62, and the terminal of permissivecontact 55 coupled to conductor 21 is connected to the common pointbetween resistors 62 and 63. The positive voltage on grid 57C renderstube 57 slightly conductive. As a result, under normal systemconditions, sufficient current liows through cathode resistor 58 toraisethe potential of the cathode of tube 56 to a value whereby tube 56is biased to cutoff.

As soon as the impedance relay operates to produce 'd voltage of tube 56increases with the signal, and tube 56 soon conducts sufficient currentto energize electromagnetic relay 54 thereby opening permissive contact55. The periody of delay in energizing relay 54 is necessary wh hasefault has occurred on the protected transmission line to permit theoutput control signal of tripping relay 19 to pass to control relay 22and complete its tripping function before permissive contact 55 opens.After electromagnetic relay 54 has been energized, a subsequent outputcontro l signal from the tripping relay, such as caused by the apparentimpedance reaching locus LT during the power swing, will by the opencircuit at permissive contact 55. The overall operating time requiredby'blocking relay 29 to open permissive contact S is selected to be lessthan the time required for the transmission line apparent impedance tochange from a value on locus LB to a value on locus LTl (for example,from point A to point A in Fig. 2a) during any power swing in theparticular electric power system. This overall operating time also isselected to time delay to be blocked be longer to produce its output c22 to respond thereto whenever any within the reach of relay 1 In thecase control signal than that of the input sign blocking relay 29, issupp missive contact 55 energized. Tube duction, and

cathode resistor 58 tion is suppressed eve than the time required bytripping relay 19' ontrol signal and by control relay' phase faultoccursA 9.

of a true fault, the positive polarity output of relay 19, which has amagnitude greater al produced in the impedance lied to grid 57e throughperbefore electromagnetic relay 54 is 57 is immediately driven to fullconthe resulting rise in voltage level acrossl will bias tube 56 wherebyconducn with full voltage on grid 56C.

In this manner, energization of relay 54 is prevented during any phasefau control signal of tripping r lt on the protected line, and theoutput elay 19 is transmitted by conductors 20 and 21 to control relay22 whereby circuit breaker 1d is trippe vent undesirable loading by thegrid circuit of tube 20 isolates the inter the voltages in the g d.Resistor 62 is required to preof the output control signal 57. Arectifier 64 in conductor nal circuits of tripping relay 19 from ridcircuit of tube 57.

By providing another normally closed permissive contact ofelectromagneti c relay 54 in the closing circuit of circuit breaker 14,and by connecting conductor 21 directly to conductor be permitted andrecl swing.

20, tripping of circuit breaker 14 can osing blocked in response to apower have shown by way of illustration a preferred embodiment of ourimpedance type blocking relay inv a protecti relays, it sho plicationsfor which our blocking relay well suited.

in the directional-comparison pilot ing system descri ing application ofMerwyn E. Hodges, Norm and Harold T. Seeley,

While we have show of our invention by tions will occur to th fore,contemplate in th lication employing distance d that there are otherapis particularly For example, the blocking relay can be used typeprotective relaybed and claimed in the aforesaid cependan A. Koss verelaying app uld be understoo n and described a preferred formillustration, many modifica- We, thereall way of ose skilled in the art.

e appended claims to cover such modifications as fall within the truespirit and scope of our invention.

What we claim as new an Patent of the d desire to secure by LettersUnited States is:

l. In a fault detecting protective relay arrangement for a polyphasealternatin having a circuit interrup tripping mea riving a firsttermined ran age and current deri g current electric power system terincluding electroresponsive ns, electronic fault detecting means fordevoltage signal in response to a first predege of relationships betweenalternating voltved from the power system, first control means, anormally deenergized electroresponsive de- .vice interconnecting firstcontrol means for convey to said first control means, sai responsive tosaid tripping means, m signal in response relationships rived from thepower system, range including said first pre control means responsive toafter a predetermine said electror of said first third control meansconnec means and op signal to disable said sec venting energization ofsaid said fault detecting means and said ing said first voltage signal dfirst control means being first voltage signal to energize said eans forproducing a second voltage to a second predetermined range of lternatingvoltage and current desaid second predetermined determined range, secondsaid second voltage signal d time interval to operably energize deviceto prevent the conveyence al to said first control means, ted to saidsecond control erable when energized by said first voltage ond controlmeans thereby preelectroresponsive device, and

between a esponsive voltage sign coupling means supplying said firstvoltage signal to said third contro sponsive to prevent ener l means andincluding permissive means reoperation of said electroresp onsive deviceto gization of said third control means.

l l 12 l 2- .An impedance type relay ln an alternating Current a secondpredetermined range lof relationships between eleCtriC PoWer systemComprising, means responsive to alternating Voltage and current derivedfromythe power alternating current derived from the system forproducsystem to produce a secondI voltage signal, said second ing aunidirectional operating voltage, means responsive predetermined rangeincluding said first predetermined to alternating current derived fromthe system for devel- 5 range, rrst control means connected to saidrelay means oping an alternating voltage related to said alternating andoperable after a predetermined time interval when current by apredetermined impedance means responsive energized by said secondvoltage signal to operably ent0 the VeCtOrlal dlfSISIlCe between Salddeveloped Voltage ergize Said electroresponsive device thereby t0prevent and an alternating Voltage deriVed from tlie system or to theutilization of said rst voltage signal for initiating Said derivedalternating Voltage alone 1n tbe absence of 10 the preselected controlfunction, second control means, said developed voltage for producing aunidirectional ieiii permissive means Comprising a normally closedstraining Voltage, means resPonSiVe to tbe difference besvvitch contactcontrolled by said electroresponsive detween said operating andrestraining voltages for produ@ vice to connect said second controlmeans to said fault ing an energizing signal whenever the differencevoltage detecting means for energization by said rst voltage is morePositiVe than a predetermined Value, an elootrosignal and to disconnectsaid second control means upon responsive deViCe, lirst Control meansresPonSiVe t0 Said opeiation of said electroresponsive device, saidsecond energizing Signal to operably energiZe said eleotroresponcontrolmeans being operable substantially instantane Sive device, ControlVoltage snPPly terminals, second Conously in response to energization bysaid first voltage trol means connected to said rst control means andSignal to disable said first Conti-01 means thereby pre- Operable Wlienenergized by control Voltage to disable venting operable energization ofsaid electroresponsive said rst control means, and coupling meansconnecting device said supply terminals to said seoond Control means and5. In a fault detecting protective relay arrangement includingPerinisSiVe means for Controlling energlZation for an alternatingcurrent electric power system having a 0f Said Second Control means 1npreselected response to circuit interrupter provided withelectroresponsive closing Operation 0f Said electroresponsive deViCe 25and tripping means, fault detecting means operable sub- 3- An impedancetype relay in an alternating Curstantially instantaneously in responseto a rst predeterrent electric PoWer Circuit Comprising, relay means re"mined ianve of relationships between alternating voltage SPODSVC O allOperating eleCtIlC quantity Ilaled t0 the and Current derived from thepower System t0 produce alternatin.y Curient 1n said Power Circuit by afirst Pre a first voltage signal means connected to said faultdedetermined impedance and reSpOriSIVo t0 a restraining 30 tecting meansfor utilizing said trst voltage signal to electric quantity comprisingthe vectorial difference beenergize the tripping inegi-ig therebytripping the circuit tween a voltage proportional to the voltage of saidpower interrupter, a normally deenergized electroresponsive de- Crollitand a Voltage related to said alternating Current vice having a switchcontact connected to supervise the by another predetermined impedance,said relay means closing means of the circuit interrupter relay meansbeine7 operable to Produce an energiZing Signal WlieneVer 35 operable inresponse to a second predetermined range of the difference between tileValues of said operating and relationships between alternating voltageand current restraining quantities exceeds a predetermined value, anderived from the power system to produce a second voltelectromagneticdevice, first control means for enerage signal, said secondpredetermined range including gizing said electromagnetic device indelayed response to said rst predetermined range, first control meansconsaid energizing signal, second control means connected iieeted tosaid relay means and operable after a predeto said iirst control meansoperable when energized to termiiied time interval when energized bysaid second disable said first control means thereby preventingenervoltage signal to operably energize said electroresponsive gizationof said electromagnetic device, control voltage device thereby toprevent closing of the circuit interrupter, supply terminals, couplingmeans interconnecting said second control means, and permissive meansconnected supply terminals and said second control means whereby to saidfault detecting means and controlled by said Said Second Control moansis energiZed by tbe Control electroresponsive device for supplying saidfirst voltage Voltage, and permissive means Controlled by Sald elctrO-signal t0 said second control means only while Said magnetic device toprevent energization of said second electroresponsive device is in itsnormally deenergized control means whenever said electromagnetic deviceis condition, said second control means being operable subenergized.stantially instantaneously in response to energization by 4. ln a faultdetecting protective relay arrangement said first voltage signal todisable said rst control means between alternating voltage and currentderived from the References Cited in the tile of this patent UNITEDSTATES PATENTS vice connected to said fault detecting means for utiliz-2509025 Warrington May 23 1950 ing said rst voltage signal to initiate apreselected i 2511680 Warrington June 13' 1950 control function, relaymeans operable in response to (lo

